The human eye's sensitivity to color is much inferior to it's ability to see panchromatic light. Unless you have a truly huge telescope, and are looking at a very bright nebula, it will always look silvery-gray at the eyepiece. The problem is complicated by the sensitivity of photographic film and CCD detectors to different wavelengths of light, it is not the same as the human eye. Astronomers also take long exposure photographs or process digital images and design their detectors and emulsions to emphasize colors differently than the human visual system does, (even some colors invisible to the human eye) because it gives them more useful information about conditions in the object they are observing.

In the very largest amateur instruments (say, 12"-36" aperture) some observers report seeing tinges of red or blue in bright emission nebulae like the Orion Nebula (M42). I've never looked through anything bigger than an 8" f/5 RFT, so I've never seen color in any deep sky object.

The exception is stars, the bright ones sometimes show color even in relatively small 'scopes. Although stars are not intrinsically very colorful--they range from blue-white, to white, to yellow, orange, and sometimes pale red, the color of a black body radiator at increasingly lower temperatures. The faint ones all look white, regardless of their real color. There are a few stars, the "carbon stars", that appear visually a deep red or garnet, due to materials in their atmospheres that tint the light. As an amateur yourself, you've probably seen some double stars with beautiful color contrasts, but that is mostly a physiological effect: the human brain distorts contrasting colors for point sources of different color very close together. Double star observers often report combinations like "green and gold", or "pink and topaz", but its all in their minds.

The only exception I can think of to this general rule in deep sky objects are the so-called planetary nebulae (gas shells surrounding aging main sequence stars.) These objects are often quite bright, and the light is usually concentrated in a point source or near-stellar appearance, and they sometimes appear blue from the ionized oxygen lines of the gas shells that surround them. This is real, not a physiological effect.

As I've gotten older, I've noticed that some of the bright blue planetaries of my youth now appear greener than I remember then. I understand this is due to a natural yellowing due to aging of the lens in the eye. Getting old sucks in so many different ways.

Planetary nebulae are the butterflies, or if you prefer, the sea slugs, of the astronomical zoo. No two are alike and they are all very colorful in big telescope images. Do a Google images on "planetary nebula" for some outrageous, but typical examples. Of course, you'll never see anything like this through an amateur 'scope.

Still, there is something to be said that you are looking at real photons emitted by real physical processes in distant regions of the galaxy. Its a thrill no photograph or digital image can give you.